Lausanne, Switzerland – Distance runner Shelby Houlihan has been banned for four years for doping by the Court of Arbitration for Sport (CAS), the Athletics Integrity Unit (AIU) said on Tuesday.

The AIU said that the CAS has dismissed Houlihan's appeal in connection with a positive test for the anabolid steroid nandrolone in December 2020 over which she was suspended in January.

Houlihan, the US record holder over 1,500 and 5,000 meters, pleaded her innocence in vain.

She said she believed the positive test came from contaminated pork which was in a burrito from a Mexican food truck she ate a few hours before the test.

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"I feel completely devastated, lost, broken, angry, confused and betrayed by the very sport that I’ve loved and poured myself into just to see how good I was," Houlihan said on Instagram.

"I want to be very clear. I have never taken any performance enhancing substances. And that includes that of which I am being accused."

Houlihan (28) now faces missing out on the Tokyo Olympics this year, the Paris Games in 2024, and two world championships, including the 2022 home edition in Eugene, Oregon.

Another American track and field athlete, hurdler Brianna McNeal, was also recently given a five-year doping ban by the CAS.